The present invention relates to a thermoplastic film that can be used to make a bag suitable for packaging coins or other objects; to the bag itself; and to a package containing coins or other objects.
Coins such as the United States twenty five cent piece known as a xe2x80x9cquarterxe2x80x9d are typically packaged and transported by financial institutions in the US in canvas bags. In Europe and in some parts of Australasia, plastic bags are typically used. Clarity is sometimes an advantage, although some of the coin bags produced in Europe are white opaque. The canvas bag plus an appropriate closure is relatively expensive. The plastic system costs less than the canvas bag plus closure.
Plastic bags for storing and transporting coins is thus convenient in the sense that polyethylene bags can be made with a relatively high transparency, important when dealing with money, and with relatively low cost. However, commercial coin bags have an inadequate combination of resistance to tear propagation, and impact resistance. Quarters in particular have a rough, xe2x80x9cserratedxe2x80x9d edge which can cut bags open on impact. When dropped or thrown during transportation, loading or unloading, these bags will sometimes break open, and some of the contents will fall out of the bag. The body of the bag can be punctured or torn, or the seals can be breached by the coins. In packaging money, where accountability is essential and any loss must be accounted for, breakage and loss of contents can present a serious problem.
An improved packaging film for coins and other abusive materials should provide adequate performance in both of the physical properties discussed above: resistance to tear (as measured by tear propagation/mil, using a standard test: ASTM D 1938); and impact resistance (as measured by instrumented impact/mil, using a standard test: ASTM D 3763-95a). Other properties, such as heat sealability (so the film can be sealed together to make a bag or pouch), flexibility, i.e. relatively low tensile modulus (so a true bag can be made), and good clarity (for visual inspection of the bag contents) are also typically desirable in many packaging applications.
The inventors have developed a film, suitable for making into a bag for holding coins or other objects, exhibiting a good combination of resistance to tear and impact resistance.
In a first aspect, a multilayer film comprises a core layer comprising a polymer selected from the group consisting of nylon 6, nylon 66, nylon 6,66, and polyamide elastomer; first and second intermediate layers, each disposed on a respective opposite side of the core layer, comprising polymeric adhesive; a first outer layer, disposed on the first intermediate layer, comprising ethylene/alpha olefin copolymer having a density less than 0.940 grams/cubic centimeter; and a second outer layer, disposed on the second intermediate layer, comprising heat sealable polymer selected from the group consisting of ethylene/alpha olefin copolymer having a density less than 0.921 grams/cubic centimeter, ethylene/vinyl acetate copolymer, ethylene/alkyl (meth)acrylate copolymer, ethylene/(meth)acrylic acid copolymer, and ionomer; wherein the film has a tear propagation/mil value (ASTM D 1938) of at least 0.45 pound-inches/mil in the longitudinal direction, and at least 0.45 pound-inches/mil in the transverse direction, and an instrumented impact/mil value (ASTM D 3763-95a) of at least 0.5 joules/mil.
In a second aspect, a bag, having a first and second panel, a bag bottom, and a bag mouth, comprises a multilayer film comprising a core layer comprising a polymer selected from the group consisting of nylon 6, nylon 66, nylon 6,66, and polyamide elastomer; first and second intermediate layers, each disposed on a respective opposite side of the core layer, comprising polymeric adhesive; a first outer layer, disposed on the first intermediate layer, comprising ethylene/alpha olefin copolymer having a density less than 0.940 grams/cubic centimeter; and a second outer layer, disposed on the second intermediate layer, comprising heat sealable polymer selected from the group consisting of ethylene/alpha olefin copolymer having a density less than 0.921 grams/cubic centimeter, ethylene/vinyl acetate copolymer, ethylene/alkyl (meth)acrylate copolymer, ethylene/(meth)acrylic acid copolymer, and ionomer; wherein the film has a tear propagation/mil value (ASTM D 1938) of at least 0.45 pound-inches/mil in the longitudinal direction, and at least 0.45 pound-inches/mil in the transverse direction, and an instrumented impact/mil value (ASTM D 3763-95a) of at least 0.5 joules/mil.
In a third aspect, an article comprises a sealed bag having a first and second panel, a bag bottom, and a sealed bag mouth, wherein the bag comprises a multilayer film comprising a core layer comprising a polymer selected from the group consisting of nylon 6, nylon 66, nylon 6,66, and polyamide elastomer; first and second intermediate layers, each disposed on a respective opposite side of the core layer, comprising polymeric adhesive; a first outer layer, disposed on the first intermediate layer, comprising ethylene/alpha olefin copolymer having a density less than 0.940 grams/cubic centimeter; and a second outer layer, disposed on the second intermediate layer, comprising heat sealable polymer selected from the group consisting of ethylene/alpha olefin copolymer having a density less than 0.921 grams/cubic centimeter, ethylene/vinyl acetate copolymer, ethylene/alkyl (meth)acrylate copolymer, ethylene/(meth)acrylic acid copolymer, and ionomer; wherein the film has a tear propagation/mil value (ASTM D 1938) of at least 0.45 pound-inches/mil in the longitudinal direction, and at least 0.45 pound-inches/mil in the transverse direction, and an instrumented impact/mil value (ASTM D 3763-95a) of at least 0.5 joules/mil; and objects inside the sealed bag.
Definitions
xe2x80x9cTear Propagationxe2x80x9d herein refers to the force required to propagate a tear from a tiny slit made by a sharp blade in a specimen of the film, measured by ASTM D 1938.
xe2x80x9cInstrumented Impactxe2x80x9d herein refers to the energy necessary to puncture a restrained specimen of film, measured by ASTM D 3763-95a.
xe2x80x9cAdhesivexe2x80x9d herein refers to polymeric adhesive, more preferably an olefin polymer or copolymer having an anhydride functionality grafted thereon and/or copolymerized therewith and/or blended therewith.
xe2x80x9cAnhydride functionalityxe2x80x9d herein refers to any form of anhydride functionality, such as the anhydride of maleic acid, fumaric acid, etc., whether grafted onto a polymer, copolymerized with a polymer, or blended with one or more polymers, and is also inclusive of derivatives of such functionalities, such as acids, esters, and metal salts derived therefrom.
xe2x80x9cCore layerxe2x80x9d herein refers to the central layer of a multi-layer film. Where the film has an even number of layers, xe2x80x9ccore layerxe2x80x9d refers to either of the two central layers of a film.
xe2x80x9cEthylene/alpha-olefin copolymerxe2x80x9d (EAO) herein refers to copolymers of ethylene with one or more comonomers selected from C4 to C10 alpha-olefins such as butene-1 (i.e., 1-butene), hexene-1, octene-1, etc. in which the molecules of the copolymers comprise long chains with relatively few side chain branches or cross-linked structures. This molecular structure is to be contrasted with conventional low or medium density polyethylenes which are more highly branched than their respective counterparts. EAO includes such heterogeneous materials as linear medium density polyethylene (LMDPE), linear low density polyethylene (LLDPE), and very low and ultra low density polyethylene (VLDPE and ULDPE); as well as homogeneous polymers (HEAO) such as TAFMER(trademark) ethylene/alpha olefin copolymers supplied by Mitsui Petrochemical Corporation and metallocene-catalyzed polymers such as EXACT(trademark) resins supplied by Exxon and AFFINITY(trademark) resins supplied by the Dow Chemical Company. EAO includes long chain branched homogeneous ethylene/alpha-olefin copolymer. An EAO can for example have a density of between 0.916 and 0.945 grams/cc.
xe2x80x9cEthylene/vinyl acetate copolymerxe2x80x9d (E/VA) herein refers to a copolymer derived from ethylene and vinyl acetate, wherein the ethylene derived units in the copolymer are present in major amounts and the vinyl acetate derived units in the copolymer are present in minor amounts.
xe2x80x9cHigh density polyethylenexe2x80x9d (HDPE) herein has a density of between 0.94 and 0.965 grams per cubic centimeter.
xe2x80x9cIntermediatexe2x80x9d herein refers to a layer of a multi-layer film which is between an outer layer and core layer of the film.
xe2x80x9cLinear low density polyethylenexe2x80x9d (LLDPE) herein has a density in the range of from 0.916 to 0.925 grams per cubic centimeter.
xe2x80x9cLinear medium density polyethylenexe2x80x9d (LMDPE) herein has a density from 0.926 grams per cubic centimeter to 0.939 grams per cubic centimeter.
xe2x80x9c(Meth)acrylatexe2x80x9d herein refers to methacrylate, or to acrylate.
xe2x80x9c(Meth)acrylicxe2x80x9d herein refers to methacrylic, or to acrylic.
xe2x80x9cNon-heat shrinkablexe2x80x9d herein is a property of a material which, when heated to a temperature of 96xc2x0 C., will exhibit a free shrink (ASTM D 2732-83) of less than 5% in the longitudinal direction, and less than 5% in the transverse direction.
xe2x80x9cOuter layerxe2x80x9d herein refers to what is typically an outermost, usually surface layer of a multi-layer film, although additional layers and/or films can be adhered to it.
xe2x80x9cPolyamidexe2x80x9d herein refers to both polyamides and copolyamides, and means a polymer in which amide linkages (xe2x80x94CONHxe2x80x94) occur along the molecular chain.
xe2x80x9cPolyamide elastomerxe2x80x9d herein refers to a block copolymer of a hard segment such as nylon 6, nylon 11 or nylon 12, and a soft segment such as a polyether or a polyester. Commercial examples include certain GRILON(trademark) and GRILAMID(trademark) resins from EMS-Chemie AG such as GRILON ELX 2112 and GRILAMID ELY 60.
xe2x80x9cPolymerxe2x80x9d herein refers to homopolymer, copolymer, terpolymer, etc. xe2x80x9cCopolymerxe2x80x9d herein includes copolymer, terpolymer, etc.
All compositional percentages used herein are calculated on a xe2x80x9cby weightxe2x80x9d basis.
xe2x80x9cLDxe2x80x9d or xe2x80x9cMDxe2x80x9d herein refers to longitudinal direction or machine direction respectively, synonymous terms for the direction of the film parallel to the path of extrusion. xe2x80x9cTDxe2x80x9d or xe2x80x9cCDxe2x80x9d herein refers to transverse or cross direction respectively, synonymous terms for the direction of the film transverse to the path of extrusion.